Preheat the oven to 375°F (190°C). Line a muffin tin with 12 paper liners. Spray a 9×5-inch loaf pan with cooking spray and line with parchment paper.
In a medium bowl, add the gluten-free flour, baking powder, baking soda, ground cinnamon, and salt. Whisk to combine. Set aside.
In a large bowl, add the bananas. Mash with a fork until smooth.
Add the vegetable oil, sour cream, brown sugar, egg and vanilla extract. Mix until combined.
Add the dry ingredients to the wet ingredients. Mix until no more streaks of flour remain.
Use a cookie scoop to portion out the muffin batter into the muffin wells. The wells should be almost filled to the top.
Bake at 375°F (190°C) for 18-22 minutes, until the muffins are domed and a toothpick inserted in the center comes out clean.
Let the muffins cool for 5 minutes before removing and placing on a wire cooling rack to finish cooling.